.middle > div {
    border: 1px solid red;
}
.middle > div>div:nth-child(2){
    padding: 10px;
}
.middle > div>div:nth-child(2)>div:nth-child(2){
    text-align: center;
}

#container {
    overflow: hidden;

    height: 500px;
    margin: 0;
    font-family: "微软雅黑";
}